Supply of air to an air-conditioning circuit of an aircraft cabin from its turboprop engine

ABSTRACT

An aircraft turboprop engine has at least a low-pressure body and a high-pressure body. The low-pressure body drives a propeller by a gearbox. The turboprop engine also includes means for supplying air to an air-conditioning circuit of an aircraft cabin, wherein the means for supplying air has at least one compressor of which the rotor is coupled to the low-pressure body. The compressor has an air inlet connected to means for bleeding air from an air inlet duct of the turboprop engine.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a National Stage of WOSN PCT/FR2015/050213, filedJan. 29, 2015, which claims priority to FRSN 14/00264, filed Jan. 31,2014.

TECHNICAL FIELD

The present invention relates to the supply of air to anair-conditioning circuit of an aircraft cabin that is equipped with atleast one turboprop engine.

BACKGROUND OF THE INVENTION

On board an aircraft, it is necessary to have air available in order tobe able to perform certain functions, such as the air conditioning ofthe cockpit and the passenger cabin or the de-icing of certaincomponents of the aircraft. At high altitudes, the oxygen becomesscarcer and the air pressure drops. This involves pressurising theaircraft cabins in order to ensure the comfort and survival of thepassengers during a flight. For this purpose, air with a minimumpressure level (in general between 0.8 and 1 bar) and a controlledtemperature (regulatory requirement) must be supplied to theair-conditioning circuit. An aircraft is thus equipped with anair-conditioning circuit that is supplied by the engine or engines ofthe aircraft, which are turboprop engines in the context of theinvention.

Typically, a turboprop engine comprises at least one low-pressure bodyand one high-pressure body, the low-pressure body driving a propulsionpropeller by means of a gearbox or reduction gearbox, normally referredto as a PGB (standing for power gearbox). The low-pressure bodycomprises a turbine rotor connected by a shaft to the propeller andoptionally to a compressor. Each other body comprises a compressor rotorconnected by a shaft to a turbine rotor.

In the prior art, the air-conditioning circuit is supplied by air takenfrom one of the compressors of the turboprop engine. This does howeverpresent drawbacks, the most significant of which are:

-   -   the pressure of the air supplied to the aircraft greatly exceeds        requirements, in particular during the climbing phase of the        aircraft, which requires protection devices in case of        overpressure and requires the air pipes to be dimensioned        accordingly,    -   the temperature of the air taken off, at the compressor, greatly        exceeds the regulatory constraint (maximum temperature on        passing through the fuel zones), which requires a cooling device        that is difficult to integrate in the nacelle (generally        referred to as a precooler) before the air is sent to the        aircraft circuit,    -   a large amount of energy is lost, which is detrimental to the        consumption and efficiency of the turboprop engine,    -   the pressure in the compressor drops on idling, which requires        either the idling level of the turboprop engine to be increased        in order to have sufficient pressure in the circuit, or air to        be taken off at two points on the compressor, which requires two        take-off ports and the same number of valves for switching the        taking of air from one point to another, which is relatively        complex. In both cases this gives rise to overconsumption of        fuel on idling.

Solutions to this problem have already been proposed. It has inparticular been proposed to supply an air-conditioning circuit with airtaken from an auxiliary heat engine of the APU (auxiliary power unit)type installed in the aircraft. However, the operation of this engine isoptimised on the ground and is therefore not efficient at altitude. Theuse thereof, except when there is an engine malfunction, involvesadditional consumption of fuel compared with the previous technique.Moreover, not all aircrafts are equipped with an engine of the APU type.

It has also been proposed to equip the aircraft with a dedicatedcompressor (dedicated to the supply of air to the cabin) driven by anelectric motor. However, this solution is not satisfactory since itgives rise to a significant increase in mass, in particular because ofthe addition of the electric motor and a larger electricity generatorfor supplying this motor.

One solution to this problem could involve driving the dedicatedcompressor by the gearbox driving the accessory equipment of the engine,generally referred to as an accessory gearbox or AGB. This accessorygearbox is coupled to the high-pressure body of the turbine engine.However, this solution would not be satisfactory either since the speedof rotation of the high-pressure body varies to such an extent accordingto the operating conditions that the speed of rotation of the rotor ofthe dedicated compressor would be too low at idle speed for thiscompressor to be capable of providing an airflow at the minimum pressurerequired for the air-conditioning circuit.

Another solution to this problem may involve driving the compressor bymeans of a power takeoff on the propulsion-propeller reduction gearbox,as described in the document FR-1.208.140-A. However, this solution hasthe same drawbacks as the previous solution since the speed of rotationof the body to which the propeller is coupled varies to such an extentaccording to the operating conditions that the speed of rotation of therotor of the dedicated compressor would be too low at idle speed forthis compressor to be capable of providing an airflow at the minimumpressure required for the air-conditioning circuit. The presentinvention proposes a simple, effective and economical solution to atleast some of the problems of the prior art.

SUMMARY

The invention proposes an aircraft turboprop engine comprising at leastone low-pressure body and one high-pressure body, the low-pressure bodydriving a propulsion propeller by means of a first gearbox, theturboprop engine further comprising means for supplying air to anair-conditioning circuit of an aircraft cabin, characterised in thatsaid supply means comprise at least one compressor, the rotor of whichis coupled to the low-pressure body, said compressor comprising an airinlet connected to means for taking off air from an air inlet sleeve ofthe turboprop engine.

It is thus not necessary to equip the turboprop engine with anair-takeoff scoop in the airflow that flows in operation around andoutside the turboprop engine. This type of scoop has the drawback ofgenerating turbulence in this airflow and of requiring specific de-icingmeans. The air supply to the compressor is thus not dependent on theairflow outside the turboprop engine.

The rotor of the compressor can be coupled to the low-pressure body bymeans of the first gearbox.

In a variant, the rotor of the compressor is coupled to the low-pressurebody by means of a second gearbox.

The present invention thus proposes new technology for the supply of airto an air-conditioning circuit of an aircraft cabin. This air issupplied by a compressor, preferably dedicated to the supply of air tothe cabin, rather than taken off from a compressor of the turbopropengine, which is less detrimental to performance. According to theinvention, the rotor of this dedicated compressor is rotated by thelow-pressure body, by means of a gearbox, such as the (first) gearboxthat connects the low-pressure body to the propulsion propeller. This isparticularly advantageous, in particular when the turboprop engine isconfigured so that the speed of rotation of its low-pressure body obeysa discrete-speed law, that is to say each speed is constant in steps.The speed of the propeller may be within a fairly restricted range sinceit may no longer be functional if it slows down too much. The speed ofrotation of the low-pressure body is in particular constant during thesame flight phase. Flight phase means a phase during which the aircraftis performing only one type of manoeuvre. Thus the speed of rotation ofthe rotor of the dedicated compressor will not depend on the operatingconditions, and the dedicated compressor will be able to provide airflowat the minimum pressure required for the air-conditioning circuit, evenat idle speed. Moreover, it is no longer necessary to provide at leasttwo air-takeoff ports on the compressor, as well as the associatedvalves, which is simpler.

The dedicated compressor may have one or a plurality of stages, each ofany type, for example an axial or centrifugal stage.

In a variant, the compressor comprises an air inlet connected toair-takeoff means between an air inlet sleeve and a compressor of theturboprop engine.

A heat exchanger, for example of the precooler type, can be installedeither between the air inlet of the dedicated compressor and the takeoffmeans, or between two compressors or two compressor stages (if it has atleast two thereof), said two compressors or two compressor stages makingup the compressor that is dedicated in particular to the supply of airto the cabin. The advantage of placing a heat exchanger in this way isthat it is more effective than at the outlet of the dedicated compressor(for the same quantity of heat discharged by the exchanger, thereduction in temperature of the air sent to the aircraft is greater).This makes it possible for example to use a smaller heat exchanger thanin the prior art.

The compressor may comprise an air outlet connected to a pipe intendedto be connected to said circuit. This pipe may be equipped with at leastone flow regulation system, for example a valve. It may be equipped witha heat exchanger, for example of the precooler type. This precooler canbe simplified and can be more compact than in the prior art because theair supplying the dedicated compressor may have a relatively lowtemperature compared with the prior art. It can moreover be envisagedthat the pressure of the air emerging from the dedicated compressor isclose to the air pressure in the conditioning circuit, and thereforerelatively low, which makes it possible to simplify the pipe and inparticular to use a pipe with a thin wall in order to obtain a saving inmass compared with the prior art.

Advantageously, the turboprop engine may comprise a pneumatic starter,an air inlet of which is connected to said pipe. In the starting phase,the rotor of the pneumatic starter is coupled to the high-pressure bodyby an accessory gearbox and supplied with air by the aircraft via saidpipe. Valves exclusively supply air to the starter. The presentinvention also makes it possible to supply the pneumatic starter via thepipes of the air-conditioning circuit.

The present invention also relates to a method for supplying air to anair-conditioning circuit of a cabin of an aircraft that is equipped withat least one turboprop engine comprising at least one low-pressure bodyand one high-pressure body, the low-pressure body driving a propulsionpropeller by means of a first gearbox, characterised in that itcomprises the steps involving taking off air from an air inlet sleeve ofthe turboprop engine, supplying at least one dedicated compressor withthe air taken off and driving a rotor of said compressor by means of thelow-pressure body of the turboprop engine. This coupling can be producedby means of the first gearbox or a second gearbox.

DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other details, features andadvantages of the invention will emerge from reading the followingdescription given by way of non-limiting example and with reference tothe accompanying drawings, in which:

FIG. 1 is a highly schematic view of an aircraft turboprop engine anddepicts means for supplying air to an air-conditioning circuit of acabin of the aircraft, according to the prior art,

FIG. 2 is a highly schematic view of an aircraft turboprop engine anddepicts means for supplying air to an air-conditioning circuit of acabin of the aircraft, according to an embodiment of the invention,

FIG. 3 is a highly schematic view of a of a gearbox for driving thededicated compressor of the air supply means according to the invention,

FIGS. 4a, 4b and 4c are highly schematic views of variants of the airsupply means of the aircraft according to the invention,

FIG. 5 is a view similar to that of FIG. 2 and depicts another variantof the invention.

DETAILED DESCRIPTION

Reference is made first of all to FIG. 1, which depicts a turbopropengine 10 according to the prior art, for an aircraft.

In this case, the turboprop engine 10 is of the double-body type andcomprises a low-pressure body 12 and a high-pressure body 14, thelow-pressure body 12 driving a propulsion propeller by means of agearbox 16 or reduction gearbox, usually referred as a PGB (powergearbox). Only the shaft 18 of the propulsion propeller is shown in FIG.1.

In this case, the low-pressure body 12 comprises only a turbine rotorconnected by a shaft to the gearbox 16. The high-pressure body 14comprises a compressor rotor connected by a shaft to a turbine rotor.The shaft of the high-pressure body 14, referred to as HP shaft 20, istubular and has the shaft of the low-pressure body 12, referred to asthe LP or power shaft 22, passing coaxially therethrough. The LP shaft22 comprises at one end a pinion (not shown) coupled by means of aseries of pinions of the gearbox 16 to the shaft 18 of the propulsionpropeller.

The turboprop engine 10 comprises a box 24 for driving accessoryequipment (referred to as the accessory box or AGB, standing foraccessory gearbox) that is coupled to the high-pressure body of theturbine engine 14, and in particular to the HP shaft, by means of aradial shaft 26. The accessory gearbox 24 is mounted in the nacelle 28of the turboprop engine 10, which is depicted schematically by arectangle in dotted lines.

The accessory gearbox 24 carries and drives a plurality of items ofequipment, including a pneumatic starter 30 which, as its nameindicates, is intended to start the turboprop engine 10 by rotating itshigh-pressure body, by means of the accessory gearbox 24 and the radialshaft 26.

The turboprop engine 10 further comprises an air inlet 32 for supplyingair to the engine, and a combustion-gas exhaust pipe 34. The turbopropengine 10 further comprises a combustion chamber 35, between the LP andHP compressors on the one hand and the HP and LP turbines on the otherhand.

The turboprop engine 10 is further equipped with means for supplying airto an air-conditioning circuit 36 of a cabin 37 of the aircraft, thesemeans comprising, according to the prior art, means for taking air fromthe turboprop engine 10. The turboprop engine 10 is equipped with twoports 38 or orifices for taking off compressed air, each of these ports38 being connected by a valve 40, 42 to a pipe 44 supplying air to thecircuit 36.

The first port 38 or upstream port (with reference to the direction offlow of the gases in the engine) makes it possible to take off air at anintermediate pressure. The valve 40 connected to this pipe 44 is of thenon-return valve type.

The second port 38 or downstream port makes it possible to take off airat high pressure. The valve 42 connected to this pipe 44 is opened whenthe pressure of the air taken off by the valve 40 is not sufficient, theair taken off by the valve 40 being prevented from being reinjectedupstream by the non-return function of the shutter of the valve 40.

The pipe 44 is equipped with a valve 46 that regulates the supplypressure of the circuit 36, and a heat exchanger 47 of the precoolertype, which is intended to lower the temperature of the air before it isintroduced into the circuit 36. The pipe 44 is further connected to anair inlet of the pneumatic starter 30 by a conduit 48 equipped with avalve 50. The pipe 44 passes through a fire-resistant partition 52before being connected to the circuit 36.

The technology depicted in FIG. 1 has numerous drawbacks describedabove.

The present invention makes it possible to overcome these drawbacks byequipping the turboprop engine with a dedicated compressor, referred toas a load compressor, the rotor of which is coupled to the low-pressurebody of the engine by means of the gearbox.

FIG. 2 depicts an embodiment of this invention in which the elementsalready described above are designated by the same reference numerals.The turboprop engine in FIG. 2 may be of the same type as that depictedin FIG. 1, or of a different type. It may for example comprise more thantwo bodies. Moreover, the low-pressure body of the turboprop engineaccording to the invention may comprise an LP compressor.

The turboprop engine 110 of FIG. 2 differs from that in FIG. 1essentially by the means for supplying air to the circuit 36.

In this case, these supply means comprise a dedicated compressor 60, therotor 61 of which is coupled by the gearbox 16 to the low-pressure body12 and in particular to the LP shaft 22. As depicted schematically inFIG. 3, the rotor shaft 61 of the compressor 60 can carry a pinion 61 ameshing with a pinion 18 a of the shaft 18 of the propeller of theturboprop engine 110, this shaft 18 carrying another pinion 18 b meshingwith a pinion 22 a of the LP shaft 22. The pinions 18 a, 18 b, 22 a, 61a are housed in the gearbox 16.

The compressor 60 comprises an air inlet 62 and an air outlet 64. In theexample depicted, the air inlet 62 is connected by a conduit 66 to theair inlet sleeve 32 of the turboprop engine 110, that is to say to theportion of the turboprop engine 110 extending between the air inlet 32and the inlet of the turbine engine 14. Relatively cool air is thustaken off by the conduit 66 in order to supply the compressor 60. Air istaken off in a predetermined zone, for example so as to limit the headlosses in the airflow in the sleeve, to prevent foreign bodies thatenter the sleeve from passing into the conduit 66, etc. The air inletsleeve preferably comprises air-takeoff means in the wall thereof (forexample the upper wall) that is closest to the gearbox 16, in order toprevent the intake of foreign bodies into the conduit 66 and to restrictthe length of said conduit.

The air outlet 64 of the compressor 60 is connected to the pipe 44supplying air to the circuit 36. As described previously, this pipe 44comprises a valve 46 that regulates the supply pressure of the circuit36, and a heat exchanger 47 of the precooler type, which is intended toreduce the temperature of the air before it is introduced into thecircuit 36. The pipe 44 is further connected to an air inlet of thepneumatic starter 30 by a conduit 48 equipped with a valve 50.

The compressor 60 used in the context of the invention (FIG. 2) may beof any type and is for example an axial compressor with one or morestages or a centrifugal compressor with one or more stages or a mixedcompressor comprising one of more axial stages and one or morecentrifugal stages.

It can also be envisaged to use more than one load compressor and forexample two load compressors connected in series.

FIGS. 4a to 4c depict variants of the invention relating in particularto the position of the heat exchanger 47. As can be seen in FIG. 4a ,the heat exchanger 47 can be mounted downstream of the compressor 60,that is to say on the pipe 44, as is the case in FIG. 2. In FIG. 4b ,the heat exchanger 47 is mounted between two compressors 60 a, 60 b.Each compressor may comprise one or more stages in order to cover theaforementioned two cases. Each stage may be an axial or centrifugalstage. In FIG. 4c , the exchanger 47 is mounted upstream of thecompressor 60, that is to say on the conduit 66 described with referenceto FIG. 2.

FIG. 5 depicts another variant of the turboprop engine 410 according tothe invention, which differs from that of FIG. 2 essentially in that therotor 61 of the compressor 60 is coupled to the LP shaft 22 not by thegearbox 16 but by another gearbox 80, which can be dedicated in order tofulfil this function of coupling the LP shaft to the rotor of compressor60. The gearbox 80 can be coupled to the LP shaft 22 by means of aradial shaft 82.

The supply of air to the circuit 36 can be achieved as follows, with anyof the embodiments of the invention described above.

After the turboprop engine 110, 410 is started up, the low-pressure body12 and its shaft 22 in general rotate at a substantially constant speed.The rotor of the compressor 60 is rotated at a substantially constantspeed, which depends in particular on the step-down coefficient of thegearbox 16, 80. The rotation of the rotor shaft 61 of the compressor 60causes the suction and take off of air by the conduit 66, as far as theair inlet 62 of the compressor 60. This air is then compressed by thecompressor 60, which supplies compressed air to the pipe 44 at apredetermined pressure. The valve 46 regulates the supply pressure ofthe circuit 36. The heat exchanger 47 makes it possible to reduce thetemperature of the air before it is introduced into the circuit 36 (FIG.4a ), before it enters the compressor (FIG. 4c ) or between twocompression phases (FIG. 4b ). Whatever the operating conditions of theturboprop engine 110, 410, the rotor shaft 61 of the compressor 60rotates at a constant speed in the case where the speed of rotation ofthe low-pressure body 12 is also constant.

The invention claimed is:
 1. An aircraft turboprop engine of a doublebody type comprising at least one low-pressure body comprising a lowpressure turbine rotor connected by a low-pressure shaft to a firstgearbox driving a propeller and one high-pressure body comprising a highpressure compressor rotor connected by a high pressure shaft to a highpressure turbine rotor, the turboprop engine further comprisingair-supplying means that supply air to an air-conditioning circuit of anaircraft cabin, wherein said air-supplying means comprise at least onededicated compressor supplying air to the cabin, a rotor of which ismechanically coupled to the low-pressure shaft of the low-pressure body,said turboprop engine being provided with a conduit which is connectedto air inlet sleeve of the turboprop engine and which feeds an air inletof said dedicated compressor with air.
 2. The turboprop engine accordingto claim 1, wherein the rotor is coupled to the low-pressure shaft ofthe low-pressure body by means of the first gearbox.
 3. The turbopropengine according to claim 1, wherein the rotor is coupled to thelow-pressure shaft of the low-pressure body by means of a secondgearbox.
 4. The turboprop engine according to claim 1, wherein a heatexchanger is either mounted on the conduit before the air inlet of thededicated compressor, or between two compressors making up the dedicatedcompressor or between two compressor stages making up the dedicatedcompressor.
 5. The turboprop engine according to claim 1, wherein thededicated compressor comprises an air outlet connected to a pipeconnected to said air-conditioning circuit, said pipe being equippedwith at least one regulation means comprising at least one valve.
 6. Theturboprop engine according to claim 5, comprising a pneumatic starter,an air inlet of which is connected to said pipe.
 7. The turboprop engineaccording to claim 5, wherein the pipe is equipped with a heatexchanger.
 8. The turboprop engine according to claim 1, wherein saidturboprop engine is configured so that a speed of rotation of thelow-pressure body is substantially constant whatever the operatingconditions.
 9. A method for supplying air to an air-conditioning circuitof a cabin of an aircraft that is equipped with at least one turbopropengine comprising at least one low-pressure body having a low-pressureshaft and one high-pressure body, the low-pressure shaft of thelow-pressure body driving a propulsion propeller by means of a firstgearbox, said method comprising the steps involving taking off air froman air inlet sleeve of the turboprop engine, supplying at least onededicated compressor with the air taken off from the air inlet sleeve,mechanically coupling a rotor of said dedicated compressor to thelow-pressure shaft of the low-pressure body of the turboprop engine todrive said rotor of said dedicated compressor, and supplying the aircompressed by said dedicated compressor to the air-conditioning circuitof the cabin of the aircraft.